Apparatus and method of improving beam shaping and beam homogenization

ABSTRACT

The present invention generally relates to an optical system that is able to reliably deliver a uniform amount of energy across an anneal region contained on a surface of a substrate. The optical system is adapted to deliver, or project, a uniform amount of energy having a desired two-dimensional shape on a desired region on the surface of the substrate. Typically, the anneal regions may be square or rectangular in shape. Generally, the optical system and methods of the present invention are used to preferentially anneal one or more regions found within the anneal regions by delivering enough energy to cause the one or more regions to re-melt and solidify.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/888,433, filed Jul. 31, 2007, which is related to U.S. patentapplication Ser. No. 11/831,830, filed Jul. 31, 2007, and U.S. patentapplication Ser. No. 11/831,838, filed Jul. 31, 2007, which are allherein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention generally relate to an apparatusand method used to manufacture a semiconductor device. Moreparticularly, the invention is directed to an apparatus and method thatis used to thermally process a substrate.

2. Description of the Related Art

The integrated circuit (IC) market is continually demanding greatermemory capacity, faster switching speeds, and smaller feature sizes. Oneof the major steps the industry has taken to address these demands is tochange from batch processing silicon wafers in large furnaces to singlewafer processing in a small chamber.

During such single wafer processing the wafer is typically heated tohigh temperatures so that various chemical and physical reactions cantake place in multiple IC devices defined in the wafer. Of particularinterest, favorable electrical performance of the IC devices requiresimplanted regions to be annealed. Annealing recreates a more crystallinestructure from regions of the wafer that were previously made amorphous,and activates dopants by incorporating their atoms into the crystallinelattice of the substrate, or wafer. Thermal processes, such asannealing, require providing a relatively large amount of thermal energyto the wafer in a short amount of time, and thereafter rapidly coolingthe wafer to terminate the thermal process. Examples of thermalprocesses currently in use include Rapid Thermal Processing (RTP) andimpulse (spike) annealing. A drawback of RTP type processes is that itheats the entire wafer even though the IC devices reside only in the topfew microns of the silicon wafer. This limits how fast one can heat upand cool down the wafer. Moreover, once the entire wafer is at anelevated temperature, heat can only dissipate into the surrounding spaceor structures. As a result, today's state of the art RTP systemsstruggle to achieve a 400° C./s ramp-up rate and a 150° C./s ramp-downrate. While RTP and spike annealing processes are widely used, currenttechnology is not ideal, and tends to ramp the wafer temperature duringthermal processing too slowly and thus expose the wafer to elevatedtemperatures for too long a period of time. These thermal budget typeproblems become more severe with increasing wafer sizes, increasingswitching speeds, and/or decreasing feature sizes.

To resolve some of the problems raised in conventional RTP typeprocesses various scanning laser anneal techniques have been used toanneal the surface(s) of the substrate. In general, these techniquesdeliver a constant energy flux to a small region on the surface of thesubstrate while the substrate is translated, or scanned, relative to theenergy delivered to the small region. Due to the stringent uniformityrequirements and the complexity of minimizing the overlap of scannedregions across the substrate surface these types of processes are noteffective for thermal processing contact level devices formed on thesurface of the substrate.

Pulsed laser anneal techniques have been used to anneal finite regionson the surface of the substrate to provide a well defined annealedand/or re-melted regions on the surface of the substrate. In general, aduring a pulse laser anneal processes various regions on the surface ofthe substrate are exposed to a desired amount of energy delivered fromthe laser to cause the preferential heating of desired regions of thesubstrate. Pulse laser anneal techniques have an advantage overconventional processes that sweep the laser energy across the surface ofthe substrate, since the need to tightly control the overlap betweenadjacently scanned regions to assure uniform annealing across thedesired regions of the substrate is not an issue, since the overlap ofthe exposed regions of the substrate is typically limited to the unusedspace between die, or “kurf” lines (e.g., lines 10A in FIG. 3).

Due to the shrinking semiconductor device sizes and stringent deviceprocessing characteristics the tolerance in the variation in the amountof energy delivered during each pulse to different devices formed on thesubstrate surface is very low. These device requirements have made thetolerance to variations in the delivered energy across the exposedsurface of the substrate to be rather small (i.e., <5% variation). Onecommon non-uniformity phenomena is called “speckle.” Speckle is thegeneration of a random intensity distribution, or “hot spots” on thesurface of the substrate, when light from a highly coherent source, suchas a laser, is scattered by the features formed on a rough surface orinhomogeneous medium. Therefore, there is a need for a pulse lasertechnique that has a desirable uniformity and reduces or minimizes theeffects of speckle on the laser annealed regions of the substrate.

To better control the pulsed laser anneal process and minimize thelateral inter-diffusion between devices the energy delivered in eachpulse needs to be relatively high and the pulse duration needs to beshort, but not short enough to damage the material exposed to the pulseof energy. Rapid heating of the exposed material can cause regions ofhigh stress in the substrate, cracks to form in the substrate, or evenejection of material from the substrate surface due to the rapidexpansion of the melted regions of the substrate. Therefore, there isneed for a pulse laser anneal system that is able to reliably deliverenergy to the surface of the substrate with minimal damage to thestructure of the substrate material.

Also, the required high energy delivered during each laser pulse canpermanently damage or greatly reduce the useable lifetime of the opticalcomponents (e.g., lenses) used to deliver and control the amount ofenergy to the surface of the substrate. Therefore, there is need forapparatus and method that can be used to deliver a high energy laserpulse that will not damage or greatly affect the useable lifetime of theoptical components used to deliver the energy to the substrate surface.

SUMMARY OF THE INVENTION

The present invention generally provide an apparatus of thermallyprocessing a substrate, comprising an energy source that has an outputand is adapted to deliver a first energy pulse, a first micro-lens arrayhaving a plurality of micro-lenses that are adapted to receive at leasta portion of the first energy pulse transmitted from the output of theenergy source, a second micro-lens array having a plurality ofmicro-lenses that are adapted to receive the at least a portion of theenergy transmitted from the first micro-lens array, a first lens that ispositioned to receive the at least a portion of the energy transmittedfrom the micro lenses in the second micro-lens array and transmit theenergy received from the second micro-lens array, and a second lens thatis positioned to receive the at least a portion of the first energypulse and cause the image received by two or more micro-lenses in thefirst micro-lens array to be at least partially different, wherein thesecond lens is adapted to improve the uniformity of the at least aportion of the first pulse transmitted by the first lens.

Embodiments of the invention further provide an apparatus of thermallyprocessing a substrate, comprising an energy source that has an outputthat is adapted to deliver a first energy pulse, a pulse stretchingdevice that comprises a first beam splitting device that is adapted tosplit the first energy pulse delivered from the energy source into afirst sub-pulse and a second sub-pulse, wherein the first sub-pulse istransferred along a first path having a first length to a beam combiningdevice, and a first plurality of mirrors that are aligned to reflect thesecond sub-pulse received from the first beam splitting device along asecond path having a second length to the beam combining device, whereinthe beam combining device is adapted to transmit the first sub-pulse andsecond sub-pulse to one or more components that are used to direct themto a surface of a substrate, a first micro-lens array having a pluralityof micro-lenses that are adapted to receive at least a portion of thefirst energy pulse, a second micro-lens array having a plurality ofmicro-lenses that are adapted to receive the at least a portion of theenergy transmitted from the first micro-lens array, a first lens that ispositioned to receive the at least a portion of the energy transmittedfrom the micro lenses in the second micro-lens array and transmit theenergy received from the second micro-lens array to one or morecomponents that are used to direct the energy received to the surface ofthe substrate, and a random diffuser that is positioned to receive atleast a portion of the first energy pulse and transmit the at least aportion of the first energy pulse to the first micro-lens array.

Embodiments of the invention further provide an apparatus of thermallyprocessing a substrate, comprising a first energy source that has anoutput that is adapted to deliver a first energy pulse, a second energysource that has an output that is adapted to deliver a second energypulse, a pulse stretching device that comprises a first beam splittingdevice that is adapted to split the first pulse delivered from theenergy source into a first sub-pulse and a second sub-pulse, and thesecond energy pulse delivered from the energy source into a thirdsub-pulse and a fourth sub-pulse, wherein the first sub-pulse and thethird sub-pulse are transferred along a first path having a first lengthto a beam combining device, and a first plurality of mirrors that arealigned to reflect the second sub-pulse and the fourth sub-pulsereceived from the first beam splitting device along a second path havinga second length to the beam combining device, a first micro-lens arrayhaving a plurality of micro-lenses that are adapted to receive at leasta portion of the first energy pulse and a portion of the second energypulse, a second micro-lens array having a plurality of micro-lenses thatare adapted to receive the at least a portion of the energy transmittedfrom the first micro-lens array, a first lens that is positioned toreceive the at least a portion of the energy transmitted from the microlenses in the second micro-lens array and transmit the energy receivedfrom the second micro-lens array, a random diffuser that is positionedto receive at least a portion of the first energy pulse and a portion ofthe second energy pulse and transmit the at least a portion of the firstenergy pulse and a portion of the second energy pulse to the firstmicro-lens array, wherein the random diffuser is adapted to receive atleast a portion of the first sub-pulse, the second sub-pulse, the thirdsub-pulse, and the fourth sub-pulse delivered from the beam combiningdevice, and a controller that is adapted to synchronize the delivery ofthe first energy pulse and the second energy pulse, wherein a compositepulse formed by summing the first energy pulse and the second energypulse over time has a pulse width that is greater than the pulse widthof the first energy pulse and the second energy pulse.

Embodiments of the invention further provide a method of thermallyprocessing a substrate, comprising positioning a substrate on asubstrate support, delivering a first energy pulse having a firstwavelength and first pulse width to a first lens from a first energysource, transmitting at least a portion of the first energy pulse to afirst micro-lens array from the first lens so that the uniformity of theimage received by two or more micro-lens is at least partiallydifferent, transmitting at least a portion of the energy received by thefirst micro-lens array to a second micro-lens array, wherein the firstmicro-lens array is adapted to increase the energy density of theportion of the energy received by the second lens array, andtransmitting at least a portion of the energy received by the secondmicro-lens array to a second lens, wherein the second lens is adapted totransmit the received energy to components that transfer the energy to aregion on the surface of the substrate positioned on the substratesupport.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments. The patent or application file containsat least one drawing executed in color. Copies of this patent or patentapplication publication with color drawing(s) will be provided by theOffice upon request and payment of the necessary fee.

FIGS. 1A-1B illustrate a schematic side view of a region on a surface ofa substrate described within an embodiment herein;

FIG. 2A illustrate a graph of concentration versus depth into a regionof a substrate illustrated in FIG. 1A that is within an embodimentherein;

FIG. 2B illustrate a graph of concentration versus depth into a regionof a substrate illustrated in FIG. 1B that is within an embodimentherein;

FIG. 3 illustrates a schematic isometric view of an energy source thatis adapted to project an amount of energy on a defined region of thesubstrate described within an embodiment herein;

FIG. 4 illustrates a schematic view of a laser anneal system accordingto an embodiment described herein;

FIG. 5 illustrates a schematic view of a dose control system that ispositioned within a laser anneal system according to an embodimentdescribed herein;

FIG. 6A illustrates a schematic view of a pulse stretcher assembly thatis positioned within a laser anneal system according to an embodimentdescribed herein;

FIG. 6B illustrate graph of pulses and sub-pulses generated in a laseranneal system illustrated in FIG. 6A according to an embodimentdescribed herein;

FIG. 6C illustrates the effect of delivering the pulses illustrated inFIG. 6B on a surface of the substrate described within an embodimentcontained herein;

FIG. 7A illustrates a schematic view of a novel version of an energysource that is positioned within a laser anneal system according to anembodiment described herein;

FIG. 7B illustrate graph of sub-pulses generated in a laser annealsystem illustrated in FIG. 7A according to an embodiment describedherein;

FIG. 7C illustrates the effect of delivering the pulses illustrated inFIG. 7B on a surface of the substrate described within an embodimentcontained herein;

FIG. 8A illustrates a schematic view of a novel version of an energysource and a pulse stretcher assembly that is positioned within a laseranneal system according to an embodiment described herein;

FIG. 8B illustrate graph of pulses and sub-pulses generated in a laseranneal system illustrated in FIG. 8A according to an embodimentdescribed herein;

FIG. 8C illustrates the effect of delivering the pulses illustrated inFIG. 8B on a surface of the substrate described within an embodimentcontained herein;

FIG. 9 illustrates a schematic side view of a beam homogenizer assemblydescribed within an embodiment herein;

FIG. 10A illustrates a schematic side view of a beam homogenizerassembly described within an embodiment herein;

FIG. 10B illustrates a schematic side view of a beam homogenizerassembly described within an embodiment herein;

FIG. 11A illustrates an non-uniform image described within an embodimentherein;

FIG. 11B illustrates a graph of the intensity versus distance across thenon-uniform image illustrated in FIG. 11A described within an embodimentherein;

FIG. 11C illustrates a graph of the intensity versus distance across thecorrected image illustrated in FIG. 11D described within an embodimentherein;

FIG. 11D illustrates an corrected image described within an embodimentherein;

FIG. 11E illustrates a graph of the intensity versus distance across theimage formed by a micro-lens that is at the center of a first micro-lensarray illustrated in FIG. 10B described within an embodiment herein;

FIG. 11F illustrates a graph of the intensity versus distance across theimage formed by a micro-lens that is at the edge of a first micro-lensarray illustrated in FIG. 10B described within an embodiment herein.

DETAILED DESCRIPTION

The present invention generally relates to an optical system that isable to reliably deliver a uniform amount of energy across an annealregion 212 (FIG. 3) contained on a surface of a substrate. In oneembodiment, the optical system is adapted to deliver, or project auniform amount of energy, or “image,” having a desired two-dimensionalshape to a desired region on the surface of the substrate. Typically,the anneal regions 212 may be square or rectangular in shape and rangein area between about 4 mm² and about 1000 mm². Generally, the opticalsystem and methods of the present invention are used to preferentiallyanneal one or more regions found within the anneal regions 212 bydelivering enough energy to cause the one or more regions to re-melt andsolidify.

In general the term “substrates” as used herein can be formed from anymaterial that can benefit from the pulse laser annealing process, suchas a material that has some natural electrical conducting ability or amaterial that can be modified to provide the ability to conductelectricity. Typical substrate materials include, but are not limited tosemiconductors, such as silicon (Si), Si_(x)Ge_(1-x) alloys, andgermanium (Ge), as well as other compounds that exhibit semiconductingproperties. Such semiconductor compounds generally include group III-Vand group II-VI compounds. Representative group III-V semiconductorcompounds include, but are not limited to, gallium arsenide (GaAs),gallium phosphide (GaP), and gallium nitride (GaN). Generally, the termsemiconductor substrates include bulk semiconductor substrates as wellas substrates having deposited layers disposed thereon. Similarly, theinvented methods can also be applied to form integrated devices, such asthin-film transistors (TFTs), on relatively thin crystalline siliconlayers formed on insulating substrates (e.g., silicon-on-insulator [SOI]substrates).

In general, pulse laser anneal type processes are used to minimizeinter-diffusion between various regions of a formed device, removedefects in the substrate material, and more evenly distribute dopants invarious regions of the substrate after performing an implant step. Thelaser anneal process generally contains one or more processing stepsthat are performed on various regions of the substrate to cause them topreferentially melt when exposed to the energy delivered from an energysource (e.g., optical system 220 in FIGS. 3 and 4A-B). In one example,the substrate properties within the anneal region(s) 212 (see FIG. 2)can be modified to allow preferential melting to create the meltingpoint contrast in desired regions of the substrate. Examples of varioustechniques that may be used to create a melting point contrast arefurther described in the co-pending U.S. patent application Ser. No.11/459,847, filed Jul. 25, 2006, which is herein incorporated byreference.

FIGS. 1A-1B illustrate cross-sectional views of an electronic device 100at different stages of a device fabrication sequence, which are intendedto illustrate one example of some of the pulse laser anneal processsteps. FIG. 1A illustrates a side view of typical electronic device 100formed on a surface 105 of a substrate 10 that has two doped regions 101(e.g., doped regions 101A-101B), such as a source and drain region of aMOS device, a gate 115, and a gate oxide layer 116. The doped regions101A-101B are generally formed by implanting a desired dopant materialinto the surface 105 of the substrate 10. In general, typical n-typedopants (donor type species) may include arsenic (As), phosphorus (P),and antimony (Sb), and typical p-type dopants (acceptor type species)may include boron (B), aluminum (Al), and indium (In) that areintroduced into the substrate 10 to form the doped regions 101A-101B.FIG. 2A illustrates an example of the concentration of the dopantmaterial as a function of depth (e.g., curve C₁), from the surface 105and into the substrate 10 along a path 103 extending through the dopedregion 101A after an implant process has been performed on the substrate10. The doped region 101A has a junction depth D₁ after the implantprocess, which may be defined as a point where the dopant concentrationdrops off to a negligible amount. It should be noted that FIGS. 1A-1Bare only intended to illustrate some of the various aspects of theinvention and is not intended to be limiting as to the type of device,type of structure, or regions of a device that may benefit from thevarious aspects of the invention described herein. As semiconductordevice sizes decrease the position and geometry of structural elementsof the electronic devices 100 formed on the surface 105 of a substrate10 may vary to improve device manufacturability or device performance.

FIG. 1B illustrates a side view of the electronic device 100 shown inFIG. 1A that is exposed to radiation “B” emitted from the an energysource, such as optical radiation from a laser. During this step desiredarea(s) of the substrate 10 are exposed to an amount of energy whichcauses the various regions of the substrate (e.g., doped regions101A-101B) to selectively melt and resolidify after the pulse ofradiation “B” has been applied. The amount of energy, the energy densityand the duration that the radiation “B” is applied can be set topreferentially melt the regions 101A and 101B to form the annealedregions 102A and 102B by knowing the desired depth of these regions, thematerials contained within these regions, the adjacent materials used toform the electronic device 100, and the heat transfer characteristics ofthe components within the formed electronic device 100. As shown inFIGS. 1B and 2B, upon exposure to the radiation “B” the remelting andsolidification of the annealed regions 102A-102B causes theconcentration of the dopant atoms (e.g., curve C₁) to more uniformlyredistributed across the region 102. Also, the dopant concentrationbetween the regions 102A-B and the substrate bulk material 121 has asharply defined boundary (i.e., a “hyper-abrupt” junction) and thusminimizes the unwanted diffusion into the substrate bulk material 121.In the example, discussed above, any damage is induced into thesubstrate 10 during the implant or other subsequent processes willpreferably drop to a negligible level.

FIG. 3 illustrates a schematic representation of a portion of the laseranneal system 250, which contains an optical system 220 that is adaptedto project an amount of energy on an anneal region 212 found on asurface of a substrate that is positioned on a substrate supportassembly 205. For example, there are 40 anneal regions 212 illustratedin FIG. 3. In general, during a pulse laser anneal processes each of theanneal regions 212 formed on the surface of the substrate 10 aresequentially exposed to a desired amount of energy delivered from theoptical system 220 to cause the preferential annealing and/or meltingwithin the anneal regions 212 of the substrate. The anneal regions 212may cover an area of between about 4 mm² (e.g., 2 mm×2 mm) and about1000 mm² (e.g., 25 mm×40 mm). It should be noted that the shape of theedges of the anneal regions 212 could be any shape without varying fromthe scope of the invention as described herein. In general, it isdesirable to deliver a pulse of energy that has a uniform energy densityper unit time (e.g., watts/mm²-sec) across the anneal region 212 so thatthe annealing process on all parts of the anneal region 212 are uniform.For example, it desirable to deliver a pulse of energy that has auniformity across the anneal region 212 that is less than about 5%,where uniformity is measured by dividing the standard deviation by themean value. The 2-D representation of the uniform pulse of energy thatis to be projected across the anneal region 212 is often called the“image” (see FIGS. 11A-11F), which ideally has a uniform energy density(FIG. 11D).

Referring to FIG. 3, in general, the areas on the surface of thesubstrate may be sequentially exposed by translating the substrate 10positioned on the substrate support assembly 205 relative to the outputof the electromagnetic radiation source (e.g., conventional X/Y stage,precision stages) and/or translating the output of the radiation source(e.g., a portion of the optical system 220) relative to the substrate.The substrate supporting components in the substrate support assembly205 are adapted to support, position, and in some cases heat thesubstrate 10. In one embodiment, a substrate support assembly 205contains one or more electrical actuators 217A, 217B (e.g., linearmotor, lead screw and servo motor) and one or more precision stages 218,which are used to control the movement and position of substrate 10. Theprecision stages may contain one or more linear slides 219 that are usedto guide and support the various substrate supporting components. In oneembodiment, the movement of a substrate support 214 in a y-direction iscontrolled by use of an electrical actuator 217A and the movement of asubstrate support 214 in an x-direction is controlled by use of anelectrical actuator 217B.

Further, it may be desirable to control the temperature of the substrateduring thermal processing by placing a surface of the substrate 10 inthermal contact with a substrate supporting surface 216 of the substratesupport 214 and a heat exchanging device 215. The heat exchanging device215 is generally adapted to heat and/or cool the substrate support 214and substrate prior to, during, or after the annealing process. In thisconfiguration, the heat exchanging device 215, such as a conventionalsubstrate heater available from Applied Materials Inc., Santa Clara,Calif. (e.g., electrically resistive heating elements, temperaturecontrolled fluid heat exchanger), and may be used to improve thepost-processing properties of the annealing regions 212 of thesubstrate. In one embodiment, the laser anneal system 250 contains apower supply 215A and resistive heating elements 215B that are inthermal contact with the substrate supporting surface 216 and are usedto pre-heat the substrate positioned thereon to a temperature betweenabout 20° C. and about 800° C. prior to performing the pulse laseranneal process. In another embodiment, the power supply and resistiveheating elements are adapted to pre-heat the substrate positioned on thesubstrate support to a temperature between about 100° C. and about 500°C. In yet another embodiment, the power supply and resistive heatingelements are adapted to pre-heat the substrate positioned on thesubstrate support to a temperature between about 200° C. and about 450°C. In yet another embodiment, the power supply and resistive heatingelements are adapted to pre-heat the substrate positioned on thesubstrate support to a temperature between about 400° C. and about 450°C. In another embodiment, it may be desirable to cool the substrate to atemperature between about −240° C. and about 20° C. prior to performingthe annealing process by use of conventional chiller type heatexchanging device (e.g., cryogenic cooling system).

FIG. 4 schematically illustrates a laser anneal system 400 that containsan optical system 220, a laser anneal processing chamber 420, and asystem controller 430. The system controller 430 is generally adapted tocontrol the various components contained within the optical system 220and the laser anneal processing chamber 420, which are discussed herein.The system controller 430 is generally designed to facilitate thecontrol and automation of the thermal processing techniques describedherein and typically may include a central processing unit (CPU) (notshown), memory (not shown), and support circuits (or I/O) (not shown).The CPU may be one of any form of computer processors that are used inindustrial settings for controlling various processes and hardware(e.g., conventional electromagnetic radiation detectors, motors, laserhardware) and monitor the processes (e.g., substrate temperature,substrate support temperature, amount of energy from the pulsed laser,detector signal). The memory (not shown) is connected to the CPU, andmay be one or more of a readily available memory, such as random accessmemory (RAM), read only memory (ROM), floppy disk, hard disk, or anyother form of digital storage, local or remote. Software instructionsand data can be coded and stored within the memory for instructing theCPU. The support circuits (not shown) are also connected to the CPU forsupporting the processor in a conventional manner. The support circuitsmay include conventional cache, power supplies, clock circuits,input/output circuitry, subsystems, and the like. A program (or computerinstructions) readable by the controller determines which tasks areperformable on a substrate. Preferably, the program is software readableby the controller and includes code to monitor and control the substratesupports position relative to the output of the laser, the amount ofenergy delivered in each electromagnetic pulse, the timing of one ormore electromagnetic pulses, the intensity as a function of time foreach pulse, the temperature of the substrate, the wavelength of eachpulse delivered from each electromagnetic source to the substrate, andany combination thereof.

The laser anneal processing chamber 420 may contain an enclosedprocessing region 427 that has one or more chamber walls 426 and anoptically transparent window 428. The laser anneal processing chamber420 may also contain the substrate support 214 discussed above. Duringprocessing, the processing region 427 may be evacuated by use of vacuumpump 424 and/or purged using an inert gas source 425 to reduce thepartial pressure of undesirable gases, such as oxygen.

Optical System

FIG. 4 also schematically illustrates one embodiment of the opticalsystem 220, which include an energy source 402, a dose control system404, a pulse stretcher assembly 406, a beam homogenizer assembly 408,and a relay optics assembly 410. As noted above, the optical system 220is adapted to repeatedly deliver a desired uniform dose of energy acrossthe anneal regions 212 to preferentially anneal and/or melt desiredareas within these regions. The system controller 430 and componentswithin the optical system 220 are used to control the timing, theduration, the profile of the pulse (e.g., energy versus time), andamount of energy delivered in each pulse to the anneal region 212. Thesystem controller 430 is also generally adapted to control the variouslaser anneal processing chamber 420 and other system componentsdiscussed above.

The amount of energy required to perform the laser anneal process on asemiconductor substrate described herein can be quite large. Forexample, the dose of energy delivered from the energy source 402 may bebetween about 1 and about 10 Joules over an 8 to 10 nanosecond (ns)pulse duration, which is equivalent to delivering an average total powerof between about 100 MW to about 1,250 MW in each pulse to the annealregion. If the anneal regions 212 have an area of between about 4 mm²and about 1000 mm² the average energy density will be between about 0.1MW/mm² and about 313 MW/mm². It should be noted that the instantaneouspower delivered at any time during each pulse may be much higher orlower than the average due to variations in the profile of the energypulse. It has been found that the high powers required to perform thepulse laser anneal process can cause the usable lifetime of the opticalcomponents used to deliver or direct the energy to the surface of thesubstrate to be significantly reduced due to damage. This induced damagecan cause the process uniformity to vary pulse-to-pulse and increase thecost-of-ownership of the system.

Energy Source Assembly

The energy source 402 is generally adapted to deliver electromagneticenergy that is used to perform the pulse laser anneal process. Typicalsources of electromagnetic energy include, but are not limited to anoptical radiation source, an electron beam source, and/or a microwaveenergy source. In one embodiment of the invention, the energy source402, such as a laser, is adapted to deliver optical radiation toselectively heat desired regions of a substrate to their melting point.Since the effectiveness of the laser anneal process is dependent on thetransmission, absorption and reflection of the energy delivered from theenergy source 402 by the material to be annealed, the wavelength (λ) orwavelengths, of the delivered energy may be tuned so that they deliver adesired amount of energy to a desired depth within the substrate. Itshould be noted that the amount of energy delivered by each photon oflight also varies as a function of wavelength (E=hc/λ), and thus theshorter the wavelength the greater the energy delivered by each photonof light. However, in some cases the substrate material, such assilicon, has an absorption edge that varies with thickness andwavelength, which limit the wavelengths that are absorbed by thesubstrate material. Therefore, depending on the thickness and type ofmaterial from which the substrate is made, the wavelength(s) of theemitted radiation may be varied to achieve the desired energy transferto the substrate to minimize damage and promote uniform heating of theexposed region of the substrate. In one embodiment, the energy source402 is adapted to deliver energy at a wavelength less than about 1064 nmto a primarily silicon containing substrate. In one embodiment, thelaser annealing processes is performed on a silicon containing substrateusing radiation that is delivered at wavelengths that are less thanabout 800 nm. In another embodiment, the wavelength of theelectromagnetic energy delivered from the energy source is about 532 nmto the primarily silicon containing substrate. In yet anotherembodiment, the wavelength of the electromagnetic energy delivered fromthe energy source is about 216 nm or about 193 nm to the primarilysilicon containing substrate. In one aspect of the invention it isdesirable to use an Nd:YAG (neodymium-doped yttrium aluminium garnet)laser that is adapted to deliver energy at a wavelength between about266 nm and about 1064 nm.

Generally, current commercial lasers are not able to deliver energiesnear the high end of the desired pulse laser anneal energy level(e.g., >2 Joules) and thus in one embodiment the outputs of multiplelasers are combined to deliver a desired amount of energy to the surfaceof the substrate. However, damage to the substrate can occur if thecharacteristics of the energy pulse used in the annealing process is notoptimized or controlled. Typically, energy pulse characteristics mayinclude but are not limited to the total amount of energy, the energyflux, the energy density, and/or the duration of the pulse. If theenergy pulse characteristics are not optimized, damage to the substrateis generally created by the stress induced due to the rapid heating ofthe melted regions on the surface of the substrate. The rapid heatingcan generate acoustic shock waves in the substrate that can causecracks, induce stress, and otherwise damage various regions of thesubstrate. It should be noted that energy pulse durations that are toolong are also undesirable since this may cause the dopants in the annealregions 212 to undesirably diffuse into adjacent regions of thesubstrate. Since current commercial lasers are generally not able todeliver pulses that have a desired duration (i.e., pulse width), asystem that can deliver energy to the surface of the substrate that hasdesirable pulse characteristics is needed.

In one embodiment, the energy source 402 is adapted to deliver energybetween about 1 and 10 joules at a pulse width between about 6 ns andabout 80 ns at a desired wavelength, such as 532 nm. In anotherembodiment, the energy source 402 is adapted to deliver energy betweenabout 1 and 10 joules at a pulse width between about 20 ns and about 30ns at a desired wavelength, such as 532 nm. In another embodiment, theenergy source 402 is adapted to deliver energy between about 1 and 10joules at a pulse width between about 8 ns and about 80 ns atwavelengths such as 748 nm and/or 1064 nm.

Dose Control System

In one embodiment of the invention, a dose control system 404 is placedbetween the energy source 402 and the processing chamber 420 to controlthe timing and amount of energy delivered to the surface of thesubstrate 10 during the laser annealing process. Generally, to improvethe reliability and the repeatability of the energy delivered from apulsed laser type of energy sources 402, the output of the pulsed lasersource is continually pulsed at a desired frequency and only a fractionof the delivered pulses are allowed to pass through the dose controlsystem 404 and make their way to the surface of the substrate. The dosecontrol system 404 can thus control the delivery of a pulse of energy ata desired time to the other components in the optical system 220.

In one embodiment, as illustrated in FIG. 5 the dose control system 404contains at least one shutter assembly 510 (e.g., two shown in FIG. 5)and an attenuator assembly 520. In general, each shutter assembly 510contains an aperture 511 that is controlled to block or allow the energydelivered from the energy source 402 to the other components in theoptical system 220. In one embodiment, as shown in FIG. 5 the dosecontrol system contains two shutter assemblies 510 that are used inconcert with each other to more safely and accurately control whichpulses are allowed to pass through the dose control system 404. Theshutter assemblies 510 may be water cooled or have a provision toreflect the delivered energy to an external energy collector (notshown), or “beam dump,” to assure that the energy delivered by theenergy source 402 doesn't overheat and cause damage to the shutterassembly components.

The dose control system 404 may also contain an attenuator assembly 520that is used to adjust the amount of energy in each pulse that exits thedose control system 404. In configurations where the energy source 402delivers partially polarized light the attenuator assembly 520 maycontain a wave plate 522 that can be rotated, or oriented, by use of anactuator 521 to preferentially alter the polarization angle of a lightwave traveling through it so that it can be partially blocked by othercomponents (e.g., polarizing cubes) in the optical system 220, and thusallows the combination of components to control the amount energydelivered to the substrate surface. In one embodiment, a Pockels Cell orother similar device, is used in place of a wave plate 522 in theattenuator assembly 520 to control the amount of transmitted energythrough the dose control system 404.

Pulse Stretcher Assembly

FIG. 6A schematically illustrates one embodiment of a pulse stretcherassembly 406 that is used to optimize the profile, or shape, of thedelivered energy as a function of time that is delivered to the surfaceof the substrate during the pulse laser annealing process. As notedabove, most conventional lasers are not able to deliver a pulse that hasa desirable profile, and thus each of the pulses delivered from theoptical system 220 to the substrate needs to be adjusted to preventdamage to the substrate and/or optimize the pulse laser anneal processresults. Examples of various pulse profiles that can be delivered to asubstrate are illustrated in the energy as a function of time graphs(i.e., pulse energy profiles 611, 711 and 811) shown in FIGS. 6C, 7C,and 8C.

As shown in FIG. 6A, the pulse stretcher assembly 406 may comprise aplurality of mirrors 601 (e.g., 16 mirrors are shown) and a plurality ofbeam splitters (e.g., reference numerals 606A-606E) that are used todelay portions of the transmitted pulse 607 delivered from the energysource 402 to provide a composite pulse that has a desirable pulsecharacteristics (e.g., pulse width and pulse profile). In one example, aspatially coherent pulse of light is delivered from a single lasersource 605A found in the energy source 402. In one embodiment, a pulse607, which is transferred from the laser source 605A and passes throughthe dose control system 404, is split into two components, or sub-pulses608A, 608B, after passing through the first beam splitter 606A.Neglecting losses in the various optical components, depending on thetransmission to reflection ratio in the first beam splitter 606A, apercentage of the energy transferred in the pulse 607 (i.e., X %) istransferred to the second beam splitter 606B in the first sub-pulse608A, and a percentage of the energy (i.e., 1−X %) of the secondsub-pulse 608B follows a path A-E (i.e., segments A-E) as it isreflected by multiple mirrors 601 before it strikes the second beamsplitter 606B. In one example, the transmission to reflection ratio ofthe first beam splitter 606A is selected so that 70% of the pulse'senergy is reflected and 30% is transmitted through the beam splitter. Inanother example the transmission to reflection ratio of the first beamsplitter 606A is selected so that 50% of the pulse's energy is reflectedand 50% is transmitted through the beam splitter. Referring to FIG. 6A,the length of the path A-E, or sum of the lengths of the segments A-E(i.e., total length=A+B+C+D+E as illustrated in FIG. 6A), will controlthe delay between sub-pulse 608A and sub-pulse 608B. In general byadjusting the difference in path length between the first sub-pulse 608Aand the second sub-pulse 608B a delay of about 1.02 nanoseconds (ns) perfoot can be realized.

Next, the energy delivered to the second beam splitter 606B in the firstsub-pulse 608A is split into a second sub-pulse 609A that is directlytransmitted to the third beam splitter 606C and a second sub-pulse 609Bthat follows the path F-J before it strikes the third beam splitter606C. The energy delivered in the second sub-pulse 608B is also splitinto a third sub-pulse 610A that is directly transmitted to the thirdbeam splitter 606C and a third sub-pulse 610B that follows the path F-Jbefore it strikes the third beam splitter 606C. This process ofsplitting and delaying each of the sub-pulses continues as each of thesub-pulses strike subsequent beam splitters (i.e., reference numerals606D-E) and mirrors 601 until they are all recombined in the final beamsplitter 606E that is adapted to primarily deliver energy to the nextcomponent in the optical system 220. The final beam splitter 606E may bea polarizing beam splitter that adjusts the polarization of the energyin the sub-pulses received from the delaying regions or from the priorbeam splitter so that it can be directed in a desired direction. In oneembodiment, a waveplate 617 is positioned before a polarizing type offinal beam splitter 606E so that its polarization can be rotated for thesub-pulses following path 615. Without the adjustment to thepolarization, a portion of the light will be reflected by the final beamsplitter and not get recombined with the other branch. In one example,all light in the pulse stretcher assembly 406 is S-polarized, and thusthe non-polarizing cube beam splitters divide incoming beams, but thefinal beam splitter, which is a polarizing cube, combines the energythat it receives. The energy in the sub-pulses following path 615 willhave its polarization rotated to P, which passes straight through thepolarizing beam splitter, while the other sub pulses following path 616are S-polarized and thus are reflected to form a combined beam. In oneembodiment, the final beam splitter 606E comprises a non-polarizing beamsplitter and a mirror that is positioned to combine the energy receivedfrom the delaying regions or from the prior beam splitter. In this case,the beam splitter will project part of the energy towards a desiredpoint, transmit another part of the energy received towards the desiredpoint, and the mirror will direct the remaining amount of energytransmitted through the beam splitter to the same desired point. Onewill note that the number of times the pulse is split and delayed may bevaried by adding beam splitting type components and mirrors in theconfiguration as shown herein to achieve a desirable pulse duration anda desirable pulse profile. While FIGS. 6A and 8A illustrate a pulsestretching design that utilizes four beam delaying regions, whichcontain a beam splitter and mirrors, this configuration is not intendedto be limiting as to the scope of the invention.

FIG. 6B illustrates an example of an energy versus time graph of varioussub-pulses 1-4, for example, sub-pulses 608A, 608B, 609A, 609B that havepassed through a two beam delaying region pulse stretcher assembly,which is similar to the first two beam delaying regions of the pulsestretcher illustrated in FIG. 6A. As shown in FIG. 6B, the pulse 607delivered to the input of the pulse stretcher assembly (FIG. 6A) has apulse width equal to period t₁. In this case, sub-pulse 1 is the firstpulse, sub-pulse 2 is the second pulse, sub-pulse 3 is the third pulse,and sub-pulse 4 is the fourth pulse that exits the pulse stretcherassembly 406. In general, the period of each of the sub-pulses will beabout t₁, since this property of the original pulse will remainrelatively unchanged due to the pulse stretching process illustrated inFIG. 6A. Referring to FIG. 6B, it follows that sub-pulse 1 traveled theshortest distance and sub-pulse 4 will have traveled the longestdistance through the pulse stretcher assembly 406. In one example, thesum of the four sub-pulses will deliver a composite energy profile 612that is spread out over a period t₂, which is longer than period t₁ ofthe initial pulse. The composite energy profile 612 will also have alower average energy per unit time than the original pulse 607. FIG. 6Cillustrates a plot of the expected temperature profile of the annealregion 212 as a function of time as it is exposed to the pulse of energydelivered in the composite energy profile 612. It should be noted thatdepending on the transmission to reflection ratio of each of theselected beam splitters in the system, the energy of the sub-pulses maybe adjusted to deliver a desired pulse profile. For example, byselecting a more transmissive, rather than reflective, combination ofbeam splitters the profile of the composite energy profile 612 will havea higher starting energy that will drop off towards the end of thecomposite profile pulse 612. It should be noted that while FIGS. 6B, 7Band 8B all illustrate rectangular shaped pulses that have the sameamplitude this is not intended to be limiting as to the scope of theinvention, since other pulse shapes may be used to deliver a compositeenergy profile 612 that has a more desirable profile.

FIG. 7A schematically illustrates another embodiment of a optical system220 that doesn't use a pulse stretcher assembly 406, but instead usesmultiple synchronized laser sources 605A-605D to deliver an optimize thepulse profile that is delivered to the surface of the substrate. In oneembodiment, energy source 402 contains a two or more energy sources,such as laser sources 605A-605D, that are adapted to deliversynchronized pulses of energy to the subsequent components in theoptical system 220. In this configuration, the output 704 of each of thelasers sources can be combined using multiple beam splitters 706,mirrors (not shown), optical prisms, and/or other similar opticalcomponents that are well known in the art, to provide a composite energyprofile 712 that has a more desirable profile. Therefore, by use of thesystem controller 430 the output of each pulse from each of the lasersources 605A-605D can be synchronized to provide a desirable compositeenergy profile 712. One will note that the amplitude and duration ofeach of the pulses delivered from each of the two or more energy sourcesmay be adjusted to provide a composite energy profile that has desirablepulse characteristics.

As illustrated in FIGS. 7A and 7B, this configuration can utilizemultiple laser sources that each deliver synchronized pulses of energythat when combined into a composite energy profile 712 creates acomposite pulse that has desirable pulse characteristics, such as adesirable pulse width and profile. In one embodiment, as shown in FIG.7B multiple lasers are each used to deliver one or more pulses that havea period t₁ and desirable peak energy level. As illustrated, thecomposite energy profile 712 created by the combination of thesynchronized pulses can be adjusted to deliver a composite pulse thathas a desirable profile and pulse duration (t₂). FIG. 7C illustrates aplot of the expected temperature profile of the anneal region 212 as afunction of time that is exposed to the pulse of energy delivered in thecomposite energy profile 712.

FIG. 8A schematically illustrates another embodiment of the presentinvention that is used to deliver a desirable pulse profile by utilizingtwo or more synchronized energy sources (e.g., laser sources 605A-605D)and a pulse stretcher assembly 406, which are each discussed above inconjunction with FIGS. 6A-6C and FIGS. 7A-7C. In this configuration, byuse of the system controller 430 the output of each of the laser sources605A-605D can be synchronized so that the composite pulse 812 (FIG. 8B)will have a desirable profile. The composite pulse 812 may contain acomposite of each of the sub-pulses created in the pulse stretcherassembly 406 for each of the synchronized pulses delivered from each ofthe laser sources 605A-605B. The profile, or shape, of the compositepulse 812 shown in FIG. 8B formed from sub-pulses 1-4 is not intended tobe limiting as to the scope of the invention since any pulse profile canbe used to provide an optimized anneal process. FIG. 8C illustrates aplot of the expected temperature profile of the anneal region 212 as afunction of time that is exposed to the pulse of energy delivered in thecomposite pulse 812.

Beam Homogenizer

In one embodiment, the optical system 220 contains a beam homogenizerassembly 408 that is used to improve the uniformity of the spread of theenergy across the square, rectangular or other shaped “image” that is tobe projected within the anneal region 212 on the surface of thesubstrate. The “image” as discussed above and used herein is a square,rectangular or other shaped 2-D representation of the energy per unittime delivered in a pulse. In general, the beam homogenizer assembly 408contains various optical components, such as lenses, apertures, or otheroptical components that are used to correct for non-uniform elements ofan “image” and thus provide a more uniform distribution energy to theannealing region 212 on the surface of the substrate. In one embodiment,the beam homogenizer assembly 408 is positioned in the optical system220 so that it will homogenize a composite energy pulse delivered fromthe pulse stretcher assembly 406 and/or a composite energy pulsedelivered from synchronized pulses delivered from the energy source 402.In one embodiment, in which multiple synchronized pulses are combined toform a composite pulse, such as described above in conjunction withFIGS. 7A-7C, multiple beam homogenizer assemblies 408 can be placed ineach of the outputs 704 of each of the laser sources to homogenize thedelivered energy before it is recombined into a composite energy profile712 (FIG. 7B).

Conventional optical projection techniques have typically utilized abeam integrator assembly 910, which contains a pair of micro-lens arrays(e.g., reference numerals 904 and 906 in FIG. 9) and lens 908 thathomogenize the energy passing through this integrator assembly. Itshould be noted that the term micro-lens array, or fly's-eye lens, isgenerally meant to describe an integral lens array that containsmultiple adjacent lenses. As designed, the beam integrator assembly 910generally works best using an incoherent source or a broad partiallycoherent source whose spatial coherence length is much smaller than asingle micro-lens array's dimensions. In short, the beam integratorassembly 910 homogenizes the beam by overlapping magnified images of themicro-lens arrays at a plane situated at the back focal plane of thelens 908. The lens 908 should be well corrected so as minimizeaberrations including field distortion. Also, the size of the imagefield is a magnified version of the shape of the apertures of the firstmicrolens array, where the magnification factor is given by F/f₁ wheref₁ is the focal length of the microlenses in the first micro-lens array904 and F is the focal length of lens 908. In one example, a lens 908that has a focal length of about 175 mm and a micro-lenses in themicro-lens array have a 4.75 mm focal length is used to form an 11 mmsquare field image. One will note that many different combinations forthese components can be used, but generally the most efficienthomogenizers will have a first micro-lens array 904 and secondmicro-lens array 906 that are identical. Since it is common in the beamintegrator assembly 910 to position the first micro-lens array 904 and asecond micro-lens array 906 a distance apart so that the energy density(Watts/mm²) delivered to the first micro-lens array 904 is increased, orfocused, on the second micro-lens array 906, this can cause damage tothe second micro-lens array 906 when the energy density exceeds thedamage threshold of the optical component and/or optical coating placedon the optical components. Typically the second micro-lens array 906 isspaced a distance d₂ from the first micro-lens array 904 equal to thefocal length of the lenslets in the first micro-lens array 904. In oneexample, each the micro-lens arrays 904, 906 contains 7921 micro-lenses(i.e., 89×89 array) that are a square shape and that have an edge lengthof about 300 microns. The lens 908, or Fourier lens, is generally usedto integrate the image received from the micro-lens arrays 904, 906 andis spaced a distance d₃ from the second micro-lens array 906.

In applications where coherent or partially coherent sources are used,various interference and diffraction artifacts can be problematic whenusing a beam integrator assembly 910, since they create high intensityregions, or spots, within the projected beam's filed of view, which canexceed the damage threshold of the various optical components.Therefore, due to the configuration of the lenses or the interferenceartifacts, the useable lifetime of the various optical components in thebeam integrator assembly 910 and system has become a key design andmanufacturing consideration.

FIG. 9 schematically illustrates one embodiment in which a randomdiffuser 902 is placed within the beam homogenizer assembly 408 so thatthe uniformity of outgoing energy A₅ is improved in relation to theincoming energy A₁. In this configuration, the incoming energy A₁ isdiffused by the placement of a random diffuser 902 prior to the energyA₂, A₃ and A₄ being received and homogenized by the first micro-lensarray 904, second micro-lens array 906 and lens 908, respectively. Therandom diffuser 902 will cause the pulse of incoming energy (A₁)delivered from the energy source 402 to be distributed over a widerrange of angles (α₁) to reduce the contrast of the projected beam andthus improve the spatial uniformity of the pulse. The random diffuser902 generally causes the light passing through it to spread out so thatthe irradiance (W/cm²) of energy A₃ received by the second micro-lensarray 906 is less than without the diffuser. The diffuser is also usedto randomize the phase of the beam striking each micro-lens array. Thisadditional random phase improves the spatial uniformity by spreading outthe high intensity spots observed without the diffuser. In general, therandom diffuser 902 is narrow angle optical diffuser that is selected sothat it will not diffuse the received energy in a pulse at an anglegreater than the acceptance angle of the lens that it is placed before.In one example, the random diffuser 902 is selected so that thediffusion angle α₁ is less than the acceptance angle of the micro-lensesin the first micro-lens array 904 or the second micro-lens array 906. Inone embodiment, the random diffuser 902 comprises a single diffuser,such as a 0.5° to 5° diffuser that is placed prior to the firstmicro-lens array 904. In another embodiment, the random diffuser 902comprises two or more diffuser plates, such as 0.5° to 5° diffuserplates that are spaced a desired distance apart to further spreading outand homogenize the projected energy of the pulse delivered from theenergy source 402. In one embodiment, the random diffuser 902 may bespaced a distance d₁ away from the first micro-lens array 904 so thatthe first micro-lens array 904 can receive substantially all of theenergy delivered in the incoming energy A₁.

Quadratic Phase Error

While beam integrator assembly configurations are generally useful tohelp homogenize light from low energy incoherent light sources, whenthey are used with spatially coherent or spatially partially coherentenergy sources that have a spatial coherence greater than approximately1/10^(th) the distance between lenses, dramatic intensity fluctuationscan occur at the edge of the image due to diffraction related effects.FIG. 11A is a two dimensional representation of a projected image, whichis intended to pictorially illustrate the uniformity fluctuations of anon-uniform image 1101 that can be created when using a spatiallycoherent energy source. The variations that are illustrated by thevarious shades of gray clearly show that the high intensity regions 1104(i.e., lighter shades of grey) are found near the edges 1102 while amore uniform and a lower intensity region is found near the centerregion 1103 of the non-uniform image 1101. FIG. 11B is a graphicalrepresentation of the intensity variation versus distance of across-section of the non-uniform image 1101 shown in FIG. 11A. In thisexample, the numerical aperture (NA) of the system is 0.00088, themagnification is 35.6, and the wavelength of the spatially coherentlight is 532 nm. The representative intensity variation versus distance,or curve 1105, has been plotted using a bisecting plane that passesthrough the center region 1103 and through the edges 1102 of thenon-uniform image 1101. The high intensity regions 1104 illustrated inFIGS. 11A and 11B, which are shown by the large peaks 1106, are believedto be created by the aberrations in the lens components, unwantedfiltering effects of the optical components in the system, interferenceeffects, and/or diffraction related effects occurring near the edge ofthe non-uniform image 1101. Since the goal of current pulse laser annealprocesses is to provide a uniform energy field that has a uniformity ofless than 5% these effects can greatly affect the usefulness of thelaser anneal process. The variation in intensity seen in a real pulsedlaser anneal system due to the coherent light effects can create highintensity regions near the edge that have a magnitude as high as about20% above the mean intensity. One way to resolve this problem is to tryto make the spatially coherent energy more incoherent, which isgenerally hard to do in practice.

Alternately, in one embodiment, as illustrated in FIG. 10A the highintensity regions of the non-uniform image 1101 are removed by theplacement of an aperture 912 within the optical path to effectivelyblock these high intensity regions. While this method can be effectiveto improve the uniformity of the non-uniform image 1101 it reduces theamount energy delivered and the effective image size E₂ of thenon-uniform image 1101 as compared to the original image size E₁ of theimage. Adding an aperture 912 can also make the optical system 220 morecomplex due to the need to make the energy source larger to account forthe decrease in delivered energy, the need to accurately position theaperture, the need to cool the aperture, and in some cases the need tomagnify the image.

Quadratic Phase Error Beam Homogenizer

FIG. 10B illustrates another embodiment of the invention that is used tocorrect intensity variations at the edge and center regions of thenon-uniform image 1101 shown in FIG. 11A. The image formed at the finalimage plane B₁ from a typical beam integrator assembly 910, discussedabove, is the average of the images formed from each micro-lens in themicro-lens arrays 904, 906, which are in fact are nearly identical. Inan uncorrected system, as shown in FIG. 9, each of the micro-lenses inthe micro-lens arrays 904, 906 produces an image that has high intensitypeak near the edge as shown in FIGS. 11A and 11B. In the example shownin FIGS. 11A and 11B, the first and second micro-lens arrays 904, 906contained 2500 micro-lenses (i.e., 50×50 array) that were square shaped(e.g., edge length of about 300 microns) and a single 175 mm focallength lens 908 were used.

To minimize the areas of high intensity light near the edge of the imagea correction lens 1001 that has a desired focal length is placed infront of the first micro-lens array 904. The correction lens 1001controls the variable amount of quadratic phase, or variable aberration,to the image received (e.g., energy G₁, energy G₁+energy G₂) andprojected (e.g., energy G₃) by each micro-lens in the micro-lens array904 to adjust the sum of each of the micro-lenses received at the imageplane B₁ so that the image is more uniform. The correction lens 1001adjusts the image projected by each micro-lens in the micro-lens arraysso that the sum of all the lenses will improve the uniformity of thecomposite image. In one embodiment, the correction lens 1001 is used toreduce the intensity fluctuations near the edge of the projected image.Part of this correction of the composite image is due to the adjustedvariation in the spatial frequency spectrum, or quadratic phase, of thelight received by each of the micro-lenses in the micro-lens array.

In one embodiment, the amount of quadratic phase added for themicro-lens near the center of the micro-lens array 904 is small, whilethe amount of quadratic phase added to the micro-lens near the edge ofthe micro-lens array 904 is large. Thus, the image formed by the imageprojected through the center of the correction lens and center of themicro-lens array is approximately the same as if no correction lens 1001is in place, while the image at the edges will have significantly morechanges from the uncorrected shape. In one embodiment, each micro-lensin the micro-lens array sees a variable amount of quadratic phasedepending on its position within the micro-lens array and thus theprojected image for each micro-lens in the micro-lens array 904 isslightly changed due to the differing curvature of the light receivedfrom the corrective lens 1001.

FIGS. 11E and 11F illustrate an example of how the shape of theintensity versus distance across the lens of a projected image from amicro-lens positioned at the center and edge of the micro-lens array904, respectively, due to the addition of the correction lens 1001. Theimage formed by a micro-lens positioned at the center of the micro-lensarray 904 and the center of the correction lens 1001 will produce animage that is approximately the same as that formed if no correctionlens was placed before the micro-lens arrays. For example, the curve1105 in FIG. 11B and curve 1111 in FIG. 11E are very similar, since theimage represented in FIG. 11B is the sum of all the uncorrectedidentical images projected by each micro-lens in the micro-lens array.However, in one example the images formed by micro-lenses near the edgeof the micro-lens arrays (see curve 1112 in FIG. 11F) will produce fewerripples and tend to have an intensity that drops off more rapidly thanthe center micro-lenses. In one embodiment, the correction lens 1001 isselected and positioned so that the projected image by each micro-lenswill gradually vary for each micro-lens that is in between the centerand the edge of the micro-lens array.

In one embodiment, micro-lenses in the micro-lens array that are spacedan equal distance from a symmetric axes of the correction lens, such asthe center of a spherical shaped correction lens will each havesimilarly shaped intensity peaks across the projected image. Forexample, for each micro-lens that is positioned an equal distance fromthe symmetric axis of the correction lens in a square micro-lens arraywill generally project the same shaped image.

By selecting a correction lens 1001 that has a proper focal length andlens shape based on the wavelength of the light, spatial coherence ofthe light, numerical aperture of the micro-lenses, the number ofmicro-lenses in the micro-lens arrays, and focal length of themicro-lens arrays, the corrected image produced will be more uniform dueto the blending of the peaks and valleys created by the corrected imageprojected by each of the micro-lenses in the micro lens array. Forexample, a more uniform composite image is formed by the summation ofthe high intensity peaks produced by some micro-lenses with lowintensity peaks generated by others. It is believed that by increasingthe number of micro-lenses in the micro-lens arrays the longer the focallength the correction lens 1001 would likely need to be to effectivelycorrect for the high intensity peaks at the edge of the corrected image1108. The careful balancing of quadratic phase change due to theproperties of the various lens in the beam homogenizer, such as focallength of the various lenses (e.g., corrective lens), will lead to amore uniform image with very little loss of transmitted energy.

FIG. 11D illustrates a corrected image 1108 that is formed by adding thecorrection lens 1001 into the optical path before the first micro-lensarray 904. In one example, the correction lens 1001 is a single 200 mmfocal length lens that is placed roughly 50 mm in front of themicro-lens array 904 that contains 2500 micro-lenses that are a squareshape and have an edge length of about 300 microns. The focal length ofa desirable correction lens will have focal length that does notincrease the angle too much for the homogenizer to accommodate, but hasa focal length long enough to introduce enough phase shift to provide adesirable uniformity. The desired focal length is a function of theacceptance angle of the homogenizer, which is related to the aperturesize of the micro-lenses in the second micro-lens array 906 divided bytwo times the focal length of the first micro-lens array 904. Thecorrection lens can be placed before (shown in FIG. 10B) or after (notshown) the random diffuser 902 in the optical path if it is needed, butbefore the first micro-lens array 904. One will note that the highintensity regions 1104 seen in FIG. 11A have almost all been removed inFIG. 11D (see reference numerals 1104A) by the addition of thecorrection lens 1001.

FIG. 11C is a graphical representation of the intensity variation versusdistance of a cross-section of the corrected image 1108 shown in FIG.11D. The representative intensity variation versus distance, or curve1109, has been plotted using a bisecting plane that passes through thecenter region 1103 and through the edges 1102 of the corrected image1108. The high intensity regions 1104 found at the edges 1102 of thecurve 1110 in FIG. 11B have been removed in FIG. 11C.

Theoretically, it is possible to calculate the intensity pattern at theback focal plane of the long focal length lens 908; however, thepresence of the random diffuser 902 makes this difficult. In any case,it is believed that the theoretical output intensity across thecorrected image 1108 can be found by using equation (1).

$\begin{matrix}{{I\left( {x,y} \right)} = {\sum\limits_{k = 1}^{K}{\sum\limits_{I = 1}^{L}{{\sum\limits_{m = 1}^{M}{\sum\limits_{n = 1}^{N}{\int_{- \frac{NA}{\lambda}}^{\frac{NA}{\lambda}}{\int_{- \frac{NA}{\lambda}}^{\frac{NA}{\lambda}}{\begin{pmatrix}{\int_{{dm}\frac{a}{2}}^{m\frac{a}{2}}{\int_{{- n}\frac{a}{2}}^{n\frac{a}{2}}{{H_{kl}\left( {x,y} \right)}{\mathbb{e}}^{{\mathbb{i}\phi}{({x,y})}}}}} \\{{\mathbb{e}}^{{\mathbb{i}}\;{\pi{({\frac{x^{2}}{\lambda\; f} + \frac{y^{2}}{\lambda\; f}})}}}{\mathbb{e}}^{{\mathbb{i}2}\;{\pi{({{x\;\xi} + {yn}})}}}{\mathbb{d}x}{\mathbb{d}y}}\end{pmatrix}{\mathbb{d}\xi}{\mathbb{d}\eta}}}}}}}^{2}}}} & (1) \\{{H_{kl}\left( {x,y} \right)} = {{H_{k}\left( \frac{\sqrt{2}x}{\omega} \right)}{H_{l}\left( \frac{\sqrt{2}y}{\omega} \right)}{\mathbb{e}}^{\frac{- {({x^{2} + y^{2}})}}{\omega^{2}}}}} & (2) \\{{\mathbb{e}}^{\mathbb{i}\phi}\left( {x,y} \right)} & (3) \\{{\mathbb{e}}^{\mathbb{i}\pi}\left( {\frac{x^{2}}{\lambda\; f} + \frac{y^{2}}{\lambda\; f}} \right)} & (4) \\{\mathbb{e}}^{{\mathbb{i}2}\;{\pi{({{x\;\xi} + {y\;\eta}})}}} & (5)\end{matrix}$

The function H_(kl)(x, y) illustrated in equation (2) is the familiarHermite polynomials that describe the laser beam, the functionillustrated in equation (3) is the phase factor imposed on the beam bythe random diffuser 902, the function illustrated in equation (4) is thequadratic phase factor added to the beam by the lens 908 and thefunction illustrated in equation (5) is the Fourier transform kernal,where λ is the wavelength, f is the focal length, ω is the frequency ofthe light, X is the position in one direction across the image, and Y isthe position in another direction across the image. The inner integralsover variables X and Y represent the field produced at the exit of asingle micro-lens in the micro-lens arrays that is square shaped and hasedge length equal to “a.” The outer integrals over ξ and η are used tocalculate the intensity at the final image plane including the spatialfiltering effect of the finite numerical aperture (NA) of the system andwavelength (λ). To achieve the overall intensity one must then sum thefields for all micro-lenses illuminated by summing over indices m and nto find the field due to a single Hermite-Gaussian mode. Squaring theabsolute value of the sum produces the intensity pattern due to a singleHermite-Gaussian mode. Finally summing over all Hermite-Gaussian modesproduces the intensity pattern produced at the final image planeincluding the effects of the random diffractive diffuser and thefocusing lens. This equation does not include the effect of systemmagnification since it is assumed to be unity, but could be done byscaling the output field and the focusing lens focal length by themagnification factor.

Relay Optics

In one embodiment, the optical system 220 contains a relay opticsassembly 410 that contains a group of optical components that are usedto direct the image that is passed from the up-stream components inoptical system 220 to the surface of the substrate that is positioned onthe substrate supporting surface 216 (FIG. 4) positioned in the laseranneal processing chamber 420. In general, the relay optics assembly 410contains a number of mirrors, lenses and other common optical componentsthat allow the position, orientation and size of the image to be set sothat it fills the annealing region 212 on the surface of the substrate.

It should be noted that the order of the components found in the opticalsystem 220 and illustrated in FIGS. 4, 5, 6A, 7A and 8A are not intendedto be limiting as to the scope of the invention, since it may bedesirable to reposition one or more of the components without affectingthe functionality of the system. In another embodiment, one or more ofthe components illustrated in FIGS. 4, 5, 6A, 7A, and 8A, such as therelay optics assembly 410 may be removed from the optical system 220 toreduce cost or system complexity without varying from the basic scope ofthe invention.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. An apparatus for thermally processing asubstrate, comprising: an energy source assembly that has an output thatis adapted to deliver a first energy pulse; a pulse stretching devicethat comprises: a first beam splitting device that is adapted to splitthe first energy pulse delivered from the energy source assembly into afirst sub-pulse and a second sub-pulse, wherein the first sub-pulse istransferred along a first path having a first length to a beam combiningdevice; and a first plurality of mirrors that are aligned to reflect thesecond sub-pulse received from the first beam splitting device along asecond path having a second length to the beam combining device; a firstmicro-lens array having a plurality of micro-lenses that are adapted toreceive at least a portion of the first energy pulse; a secondmicro-lens array having a plurality of micro-lenses that are adapted toreceive at least a portion of the energy transmitted from the firstmicro-lens array; a first lens that is positioned to receive the atleast a portion of the energy transmitted from the micro lenses in thesecond micro-lens array and transmit the energy received from the secondmicro-lens array to one or more components that are used to direct theenergy received to a surface of the substrate; a second lens that ispositioned to receive at least a portion of the first energy pulse andcause one or more images received by the micro-lenses in the firstmicro-lens array to vary for two or more micro-lenses between a centerand an edge of the first micro-lens array; and a random diffuser that ispositioned to receive at least a portion of the first energy pulse andtransmit the at least a portion of the first energy pulse to the firstmicro-lens array.
 2. The apparatus of claim 1, wherein the first beamsplitting device is insensitive to a polarization of an energy deliveredin the first energy pulse and the beam combining device is adapted toorient the polarization of the first sub-pulse or the second sub-pulseto provide a composite pulse that is a sum of the first sub-pulse andthe second sub-pulse.
 3. The apparatus of claim 2, wherein the randomdiffuser is positioned to receive the at least a portion of the firstenergy pulse from the second lens.
 4. The apparatus of claim 1, whereinthe beam combining device is adapted to transmit the first sub-pulse andsecond sub-pulse to the random diffuser.
 5. The apparatus of claim 1,wherein the first length is shorter than the second length.
 6. Theapparatus of claim 1, wherein the pulse stretching device furthercomprises: a second beam splitting device that is adapted to receive andsplit the first sub-pulse into a third sub-pulse and a fourth sub-pulse,and receive and split the second sub-pulse into a fifth sub-pulse and asixth sub-pulse, wherein the third and fifth sub-pulses are transferredalong a portion of the first path to the beam combining device; a secondplurality of mirrors that are aligned to reflect the fourth sub-pulseand the sixth sub-pulse received from the second beam splitting devicealong a third path having a third path length to the beam combiningdevice; and the beam combining device that is adapted to receive thethird sub-pulse and fifth sub-pulse from the second beam splittingdevice and the fourth sub-pulse and the sixth sub-pulse from the secondplurality of mirrors.
 7. The apparatus of claim 1, wherein the energysource assembly comprises: a first energy source that is adapted todeliver a first portion of the first energy pulse; a second energysource that is adapted to deliver a second portion of the first energypulse; and a controller that is adapted to offset the delivery of thefirst portion and the second portion in time.
 8. The apparatus of claim1, wherein the second lens has an optical property causing the one ormore images received by the micro-lenses in the first micro-lens arrayto vary for two or more micro-lenses between the center and the edge ofthe first micro-lens array by varying a quadratic phase error.
 9. Anapparatus for thermally processing a substrate, comprising: a firstenergy source that has an output that is adapted to deliver a firstenergy pulse; a second energy source that has an output that is adaptedto deliver a second energy pulse; a pulse stretching device thatcomprises: a first beam splitting device that is adapted to split thefirst pulse delivered from the energy source into a first sub-pulse anda second sub-pulse, and the second energy pulse delivered from theenergy source into a third sub-pulse and a fourth sub-pulse, wherein thefirst sub-pulse and the third sub-pulse are transferred along a firstpath having a first length to a beam combining device; and a firstplurality of mirrors that are aligned to reflect the second sub-pulseand the fourth sub-pulse received from the first beam splitting devicealong a second path having a second length to the beam combining device;a first micro-lens array having a plurality of micro-lenses that areadapted to receive at least a portion of the first energy pulse and aportion of the second energy pulse; a second micro-lens array having aplurality of micro-lenses that are adapted to receive at least a portionof the energy transmitted from the first micro-lens array; a first lensthat is positioned to receive the at least a portion of the energytransmitted from the micro lenses in the second micro-lens array andtransmit the energy received from the second micro-lens array; a secondlens that is positioned to receive at least a portion of the firstenergy pulse and cause one or more images received by the micro-lensesin the first micro-lens array to vary for two or more micro-lensesbetween a center and an edge of the first micro-lens array; a randomdiffuser that is positioned to receive at least a portion of the firstenergy pulse and a portion of the second energy pulse and transmit theat least a portion of the first energy pulse and a portion of the secondenergy pulse to the first micro-lens array, wherein the random diffuseris adapted to receive at least a portion of the first sub-pulse, thesecond sub-pulse, the third sub-pulse, and the fourth sub-pulsedelivered from the beam combining device; and a controller that isadapted to synchronize the delivery of the first energy pulse and thesecond energy pulse, wherein a composite pulse formed by summing thefirst energy pulse and the second energy pulse over time has a pulsewidth that is greater than a pulse width of the first energy pulse andthe second energy pulse.
 10. The apparatus of claim 9, furthercomprising a processing chamber that comprises: one or more walls thatenclose a processing region, wherein one of the one or more walls isadapted to transmit at least a portion of the energy delivered in thefirst energy pulse and the second energy pulse; a substrate supportsupporting a substrate that is positioned to receive at least a portionof the energy transferred in the first energy pulse and the secondenergy pulse through the one of the one or more walls; and a heatexchanging device that is adapted to heat the substrate positioned onthe substrate support.
 11. The apparatus of claim 9, further comprisinga shutter that is adapted to selectively allow the first and secondenergy pulses to be transferred to the pulse stretching device by use ofthe controller.